The patch halves space occupied by compound_dtor and compound_order in
struct page.
For compound_order, it's trivial long -> int/short conversion.
For get_compound_page_dtor(), we now use hardcoded table for destructor
lookup and store its index in the struct page instead of direct pointer
to destructor. It shouldn't be a big trouble to maintain the table: we
have only two destructor and NULL currently.
This patch free up one word in tail pages for reuse. This is preparation
for the next patch.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
include/linux/mm.h | 22 +++++++++++++++++-----
include/linux/mm_types.h | 11 +++++++----
mm/hugetlb.c | 8 ++++----
mm/page_alloc.c | 9 ++++++++-
4 files changed, 36 insertions(+), 14 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 2e872f92dbac..9c21bbb8875a 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -575,18 +575,30 @@ int split_free_page(struct page *page);
/*
* Compound pages have a destructor function. Provide a
* prototype for that function and accessor functions.
- * These are _only_ valid on the head of a PG_compound page.
+ * These are _only_ valid on the head of a compound page.
*/
+typedef void compound_page_dtor(struct page *);
+
+/* Keep the enum in sync with compound_page_dtors array in mm/page_alloc.c */
+enum {
+ NULL_COMPOUND_DTOR,
+ COMPOUND_PAGE_DTOR,
+ HUGETLB_PAGE_DTOR,
+ NR_COMPOUND_DTORS,
+};
+extern compound_page_dtor * const compound_page_dtors[];
static inline void set_compound_page_dtor(struct page *page,
- compound_page_dtor *dtor)
+ unsigned int compound_dtor)
{
- page[1].compound_dtor = dtor;
+ VM_BUG_ON_PAGE(compound_dtor >= NR_COMPOUND_DTORS, page);
+ page[1].compound_dtor = compound_dtor;
}
static inline compound_page_dtor *get_compound_page_dtor(struct page *page)
{
- return page[1].compound_dtor;
+ VM_BUG_ON_PAGE(page[1].compound_dtor >= NR_COMPOUND_DTORS, page);
+ return compound_page_dtors[page[1].compound_dtor];
}
static inline int compound_order(struct page *page)
@@ -596,7 +608,7 @@ static inline int compound_order(struct page *page)
return page[1].compound_order;
}
-static inline void set_compound_order(struct page *page, unsigned long order)
+static inline void set_compound_order(struct page *page, unsigned int order)
{
page[1].compound_order = order;
}
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 58620ac7f15c..63cdfe7ec336 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -28,8 +28,6 @@ struct mem_cgroup;
IS_ENABLED(CONFIG_ARCH_ENABLE_SPLIT_PMD_PTLOCK))
#define ALLOC_SPLIT_PTLOCKS (SPINLOCK_SIZE > BITS_PER_LONG/8)
-typedef void compound_page_dtor(struct page *);
-
/*
* Each physical page in the system has a struct page associated with
* it to keep track of whatever it is we are using the page for at the
@@ -145,8 +143,13 @@ struct page {
*/
/* First tail page of compound page */
struct {
- compound_page_dtor *compound_dtor;
- unsigned long compound_order;
+#ifdef CONFIG_64BIT
+ unsigned int compound_dtor;
+ unsigned int compound_order;
+#else
+ unsigned short int compound_dtor;
+ unsigned short int compound_order;
+#endif
};
#if defined(CONFIG_TRANSPARENT_HUGEPAGE) && USE_SPLIT_PMD_PTLOCKS
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index a8c3087089d8..8ea74caa1fa8 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -969,7 +969,7 @@ static void update_and_free_page(struct hstate *h, struct page *page)
1 << PG_writeback);
}
VM_BUG_ON_PAGE(hugetlb_cgroup_from_page(page), page);
- set_compound_page_dtor(page, NULL);
+ set_compound_page_dtor(page, NULL_COMPOUND_DTOR);
set_page_refcounted(page);
if (hstate_is_gigantic(h)) {
destroy_compound_gigantic_page(page, huge_page_order(h));
@@ -1065,7 +1065,7 @@ void free_huge_page(struct page *page)
static void prep_new_huge_page(struct hstate *h, struct page *page, int nid)
{
INIT_LIST_HEAD(&page->lru);
- set_compound_page_dtor(page, free_huge_page);
+ set_compound_page_dtor(page, HUGETLB_PAGE_DTOR);
spin_lock(&hugetlb_lock);
set_hugetlb_cgroup(page, NULL);
h->nr_huge_pages++;
@@ -1117,7 +1117,7 @@ int PageHuge(struct page *page)
return 0;
page = compound_head(page);
- return get_compound_page_dtor(page) == free_huge_page;
+ return page[1].compound_dtor == HUGETLB_PAGE_DTOR;
}
EXPORT_SYMBOL_GPL(PageHuge);
@@ -1314,7 +1314,7 @@ static struct page *alloc_buddy_huge_page(struct hstate *h, int nid)
if (page) {
INIT_LIST_HEAD(&page->lru);
r_nid = page_to_nid(page);
- set_compound_page_dtor(page, free_huge_page);
+ set_compound_page_dtor(page, HUGETLB_PAGE_DTOR);
set_hugetlb_cgroup(page, NULL);
/*
* We incremented the global counters already
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index df959b7d6085..beab86e694b2 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -208,6 +208,13 @@ static char * const zone_names[MAX_NR_ZONES] = {
"Movable",
};
+static void free_compound_page(struct page *page);
+compound_page_dtor * const compound_page_dtors[] = {
+ NULL,
+ free_compound_page,
+ free_huge_page,
+};
+
int min_free_kbytes = 1024;
int user_min_free_kbytes = -1;
@@ -437,7 +444,7 @@ void prep_compound_page(struct page *page, unsigned long order)
int i;
int nr_pages = 1 << order;
- set_compound_page_dtor(page, free_compound_page);
+ set_compound_page_dtor(page, COMPOUND_PAGE_DTOR);
set_compound_order(page, order);
__SetPageHead(page);
for (i = 1; i < nr_pages; i++) {
--
2.5.0
--
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